A planted aquarium needs substrate, lighting, and CO2 to work

A planted aquarium is a tank where live plants grow underwater alongside fish. Unlike a bare tank, plants need three things to survive: a substrate (the material on the bottom) that holds nutrients, light strong enough to reach the plants, and carbon dioxide. The plants then produce oxygen, which helps the fish, and they consume nitrates that would otherwise build up and harm the water quality. You do not need special equipment to start—most planted tanks begin with basic aquarium gear plus a few additions.

The difference between a planted tank and a regular one is mainly in what sits on the bottom and above the tank. A standard aquarium might have gravel and a basic light. A planted tank has nutrient-rich substrate and a light rated for plant growth, usually measured in lumens or kelvin temperature. Some planted tanks also use a CO2 system to speed plant growth, though many beginners skip this step and still see results.

Key Takeaways

  • Substrate for planted tanks should be at least two inches deep and contain nutrients; common choices are aqua soil, flourite, or a layered base with potting soil underneath.
  • Lighting must be strong enough for plant photosynthesis—typically 8 to 10 hours per day, with LED lights rated 6500K to 7000K color temperature working well for most plants.
  • Fertilizers replace nutrients that plants consume; liquid all-in-one fertilizers are simpler for beginners than separate nitrogen, phosphorus, and potassium bottles.
  • CO2 injection speeds growth but is optional; many planted tanks thrive without it if you choose hardy plants and dose fertilizer regularly.
  • Plants should be planted in clusters, not scattered, and given two to four weeks to establish before adding fish.

Choosing and preparing the right substrate

The substrate is where plant roots anchor and absorb nutrients. Standard aquarium gravel does not hold enough nutrients for plants to thrive, so planted tanks use specialized substrates. Aqua soil is the most popular choice—it is a clay-based material that holds nutrients and lowers pH slightly, which many aquatic plants prefer. Brands like ADA Aqua Soil and Flourite are widely available. A bag typically covers a 10-gallon tank to a depth of two inches.

If aqua soil is too expensive, you can layer the bottom: put an inch of potting soil (the kind used for houseplants, not garden soil) on the very bottom, then cap it with two inches of inert substrate like sand or gravel on top. The potting soil layer stays in place because the cap holds it down. This method costs less but requires careful setup so the potting soil does not cloud the water during filling.

Depth matters. Two to three inches of substrate gives roots room to spread and holds enough nutrients to last several months. Shallower substrate means plants struggle and you fertilize more often. When you pour substrate into the tank, slope it slightly higher toward the back—this creates visual depth and makes the tank easier to clean later.

Installing lighting that plants can use

Plants need light to photosynthesize, and standard aquarium lights are often too dim. Look for LED lights rated between 6500K and 7000K color temperature—this range mimics natural daylight and is what most aquatic plants evolved under. The brightness should be measured in lumens or PAR (photosynthetically active radiation), though lumens is easier to find on product labels. For a 20-gallon tank, aim for at least 1000 to 1500 lumens.

Run the light 8 to 10 hours per day. Set a timer so the light turns on and off at the same time each day—this mimics a natural day-night cycle and prevents algae blooms, which happen when light runs too long. Many planted tank keepers use a straightforward plug-in timer from a hardware store, set to 8 hours for the first month, then increase to 10 hours once plants are established.

Position the light so it shines evenly across the tank. Lights mounted on the rim or hanging above the tank work better than lights built into the hood, because they sit closer to the water surface and deliver more light to the plants below. If your light has a dimmer, start at 50 percent brightness for the first two weeks, then increase gradually—this prevents algae from taking over before plants are strong enough to compete.

Adding fertilizers to replace what plants consume

As plants grow, they pull nitrogen, phosphorus, potassium, and trace minerals from the water. Even if you have fish in the tank, their waste does not always provide enough of these nutrients in the right balance. Fertilizers replace what the plants use. For beginners, an all-in-one liquid fertilizer is simpler than buying separate bottles of nitrogen, phosphorus, and potassium.

Dose fertilizer once or twice per week, following the bottle instructions—most recommend a few milliliters per 10 gallons. Do a partial water change (25 to 50 percent) once a week before you fertilize; this removes excess nutrients and keeps the water clean. If you see brown or yellow leaves on plants, or if growth slows after the first month, increase the fertilizer dose slightly.

Some planted tanks also use root tabs—small pellets you push into the substrate near plant roots. Root tabs release nutrients slowly over weeks and are useful for heavy feeders like sword plants or crypts. For a beginner tank with straightforward plants like anubias or java fern, liquid fertilizer alone is usually enough.

Deciding whether to use CO2 injection

CO2 injection is a system that bubbles carbon dioxide into the tank, speeding plant growth and allowing you to keep more demanding plants. A basic CO2 kit includes a pressurized cylinder, a regulator, a diffuser, and tubing. It costs $150 to $300 to set up. Many beginner planted tanks skip CO2 and still succeed, especially if you choose hardy, slow-growing plants.

Without CO2, plants grow more slowly but still grow. Plants like anubias, java fern, and moss do well in low-CO2 tanks. Plants like stem plants (ludwigia, rotala) and carpeting plants (dwarf hairgrass, monte carlo) grow faster with CO2 but can survive without it if you fertilize regularly and keep light strong. If you want to add CO2 later, you can—it is not a decision you have to make at the start.

If you do use CO2, install a drop checker—a small device that floats in the tank and changes color to show CO2 levels. Aim for 1 to 2 bubbles per second from the diffuser as a starting point, then adjust based on the drop checker reading. Too much CO2 can harm fish, so monitoring is important.

Planting and cycling the tank

Before you add fish, plant the tank and let it run for two to four weeks. This period, called the cycling phase, lets beneficial bacteria colonize the substrate and filter, and it gives plants time to root and start growing. During this time, the tank will look sparse—resist the urge to add fish early.

Plant in clusters rather than scattering plants around the tank. Group three to five stems of the same plant together; this creates visual impact and makes the tank look fuller faster. Bury the roots of stem plants (plants with long stalks) in the substrate, leaving the leaves above the surface. For plants like anubias and java fern, tie them to rocks or driftwood with fishing line—do not bury the rhizome (the thick horizontal stem), or it will rot.

During the cycling phase, do a 25 percent water change once a week. This removes decaying plant matter and keeps ammonia from building up. After four weeks, test the water with a kit that measures ammonia, nitrite, and nitrate. If ammonia and nitrite are both zero, the tank is cycled and ready for fish. If they are still present, wait another week and test again.

Choosing plants that match your setup

Hardy, beginner-friendly plants are the best starting point. Anubias and java fern are nearly impossible to kill—they grow slowly, tolerate low light, and do not need CO2. Moss (java moss, christmas moss) is also forgiving and creates a natural look. Ludwigia and rotala are stem plants that grow faster and add color, but they need stronger light and fertilizer.

Avoid plants labeled "difficult" or "high-light" until you have run a planted tank for a few months. Plants like dwarf hairgrass and monte carlo are popular for carpeting the foreground, but they need strong light and CO2 to thrive—many beginners struggle with them. Start with straightforward plants, get comfortable with the routine, then experiment with harder ones.

Buy plants from a reputable aquarium store or online retailer. When they arrive, rinse them gently under tap water to remove algae and snails, then plant them when ready. Some plants arrive emersed (grown above water) and will lose their leaves when submerged—this is normal, and new underwater leaves will grow within a few weeks.

Frequently Asked Questions

Can I use regular potting soil as my entire substrate?

No. Potting soil clouds the water and breaks down over time, creating a mess. Use it only as a bottom layer capped with at least two inches of inert material like sand or gravel. The cap keeps the potting soil in place and the water clear.

How long does it take to see plant growth?

Slow-growing plants like anubias and java fern show new leaves in two to three weeks. Faster plants like ludwigia and rotala can grow an inch per week once they are established. Growth slows in the first two weeks while roots develop, then speeds up after that.

What happens if I add fish before the plants are established?

Fish waste adds ammonia and nitrates to the water, which can cause algae blooms if plants are not yet strong enough to consume them. Wait at least two to four weeks so plants develop roots and start competing with algae for nutrients.

Do I need a CO2 system to have a planted tank?

No. Many planted tanks thrive without CO2 if you choose hardy plants, provide strong lighting, and dose fertilizer regularly. CO2 lets you keep more demanding plants and speeds growth, but it is not required to start.

Why are my plants turning brown or yellow?

Brown or yellow leaves usually mean nutrient deficiency, weak lighting, or old leaves dying naturally. Check that your light is on 8 to 10 hours per day, increase fertilizer dose slightly, and remove dead leaves by hand. New growth should be green within a week or two.